You mean, Popeye's can of spinach?
The simple thing would be to just make it a Potion of Bull's Strength.
If you are going for Popeye emulation, Popeye is already a very strong man in the source material, quite capable of defeating several ordinary men in a fight while maintaining a running banter with himself. It just is the case that strong as he is, Bluto is bigger and stronger.
However, when Popeye eats his spinach, he becomes fantastically much stronger than his already superhuman self. To simulate this, when Popeye eats his spinach, the effect is that his strength doesn't merely increase by +4, but that his strength actually doubles. Whether this is an effect of the can of Spinach, or an attribute of Popeye is a matter of debate. However, in many of the cartoons Bluto and Popeye are friends, and in at least a few (that don't involve Olive Oil) they end up as allies rather romantic rivals. There are cases of Bluto being forced to eat Spinach and undergoing the same transformation, which suggests Spinach is Magic in Popeye-verse.